Lennart Augustsson wrote: > Btw, this reminds me again that I'd like to be able to use _ in type > signatures. > With the meaning of _ being, "there's a type here, but I can't be > bothered to write it out in full."
you're not alone ... what is the meaning of two _ in one expression? do they necessarily denote the same type? (probably not.) what about type classes? for example, given sort :: Ord a => [a] -> [a], would it be ok to write sort :: [ _ ] -> [ _ ] (that is, omitting the context) or is it more like sort :: _ => [ _ ] -> [ _ ] BTW, this "_ for context" would be useful on its own! I have several cases where the conxtext for the type decl is longer than the implementation of the function. Well, nearly. With previous ghc versions, I could get this effect by omitting the type decl but writing f ( x :: type1) ( y :: type2 ) = ... I sometimes wish haddock would understand that. (*) Because - if you write a haddoc comment for a type declaration, then you don't have names for the function's arguments. This leads to either awkward prose (random example, from Data.Maybe:) > The maybe function takes a default value, a function, and a Maybe > value. If the Maybe value is Nothing ... (this only works here because all the argument types are different in this case) or you have to re-invent names, random example: > approxRational :: RealFrac a => a -> a -> Rational > approxRational, applied to two real fractional numbers x and epsilon, which looks like duplication of work. (*) of course the full form would include the return type fun (x :: type1 ) (y :: type2) :: type3 = ... I expect strong opposition from those who write functions with pattern matching (then there is a group of declarations and which one should be type-annotated?) but that's bad style anyway since constructors should not be exported :-) Best regards, -- -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- ---- http://www.imn.htwk-leipzig.de/~waldmann/ ------- _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
